A small rebellion is rising at Chelsea as the club that used to hail Cesar Azpilicueta are now looking to topple him in favour of the returning youngster Reece James.Outside of only Eden Hazard and N’Golo Kante, Azpilicueta has arguably been Chelsea’s best performer since he joined the club from Marseille for just £7 million ($8.7m) in 2013. However, he has not looked himself in recent weeks.Opposition teams are now targeting the 30-year-old right-back, with Manchester United, Norwich City and Sheffield United having all focused their attention on exposing Chelsea’s new club captain this season. Article continues below Editors’ Picks What is Manchester United’s ownership situation and how would Kevin Glazer’s sale of shares affect the club? Ox-rated! Dream night in Genk for Liverpool ace after injury nightmare Messi a man for all Champions League seasons – but will this really be Barcelona’s? Are Chelsea this season’s Ajax? Super-subs Batshuayi & Pulisic show Blues can dare to dream United used the pace of Marcus Rashford and Anthony Martial to devastating effect, their nine-second counterattacks made possible by the huge spaces left in behind the Blues backline by Azpilicueta, who had permission to come forward.Sheffield United, meanwhile, used their novel over-lapping wing-backs to attack Azpilicueta and it was no surprise that their 89th-minute equaliser at Stamford Bridge came from a cross down the Spaniard’s side of the pitch.In the Premier League, 32 per cent of the shots Chelsea have faced have been taken on Azpilicueta’s flank, compared to just 8% on the left-hand side, which is protected by Emerson Palmieri.Of course, Chelsea haven’t defended particularly well in general; only Norwich (10) have conceded more goals than Chelsea (nine) in the Premier League this term. So, Lampard knows full well that his main challenge right now is to tighten up the defence.Kante and Antonio Rudiger’s return should offer some relief but the problems appear to be rooted in tactics rather than personnel.Frank Lampard’s 4-3-3 formation sees the full-backs play high and wide, asked to push forward at every possible opportunity.Azpilicueta is certainly delivering from an offensive perspective, as his 19 crosses rank him sixth in the division with a Premier League high success rate of 52.63%.Just like Liverpool’s full-backs, Azpilicueta is supposed to help in winning the ball through pressing high up the pitch. However, this added emphasis on taking up more advanced positions has opened up gaps in behind.Chelsea’s adventurous approach has led to Azpilicueta being involved in 11.3 duels per-game – his highest ever average at Stamford Bridge. Unsurprisingly, he is fouling more than ever before and his pass accuracy has dropped below an average of 80% to 78.7% for the first time in a Blues shirt.The net result is that Chelsea’s press has been easily bypassed and Azpilicueta’s advanced defending has left space in behind for wingers such as Rashford to exploit.However, there has also been too big a gap between the midfield and the back four, which playmakers such as Emi Buendia and James Maddison have capitalised on.Azpilicueta was a left-back under Jose Mourinho, a centre-back for Antonio Conte and his now going forward more than he was under Maurizio Sarri. He is the definition of versatile but this latest change in role is proving his most difficult transition yet.His latest outing means that he has now entered the top-40 list for all-time appearances at Chelsea (288), ahead of the likes of Joe Cole, Gary Cahill and Michael Essien, and this after his busiest season to date: 53 starts, 57 matches and 4866 minutes.So, despite the initial signs of struggle last year, it is a credit to Azpilicueta’s diet, injury prevention and training regime that he is a constant in west London.Former Blues goalkeeper Mark Schwarzer knows about longevity after making over 500 Premier League appearances – more than any overseas player.He has trained alongside both Lampard and Azpilicueta and believes that both just need time to adjust.”Gym work and looking after yourself – those are things that Azpilicueta has been brilliant at and he has delivered on the football pitch,” Schwarzer told Goal.”The first couple of performances at a new-look Chelsea side under a new manager have seen Azpilicueta not at the level in the past. Part of that, though, is because the level in the past was so high.“I think it is going to take a period of adjustment. You have got a whole load of young players in the side who have played in the Premier League like Christensen and Kurt Zouma.”Some don’t know if they are in there because of injuries or whether the manager has just decided to play you and you can keep that position. At the start of the season, they know they are the number one pairing and it is up to them to stake their claim.”Rudiger is coming back fit in a couple of weeks and it is up to them to keep them out of the team. That’s a different prospect, that’s an experience thing. It is not just the pairing. It is the whole team, the combination work and the people in front of them.”You don’t just defend as a back four or five. You defend as a whole team. If you don’t have cover in front of you, then you can be exposed. There are errors there and individual errors at Manchester United.”I was at the Norwich game and for all the endeavour, they expose themselves to be countered. That happened a couple of times. Again, it is about finding that balance and making sure they get that spot on.”It’s certainly of the utmost importance. At present, Lampard’s side are on course to concede more goals than Sarri’s across the entirety of last season (39) by matchday 16.Of course, he could place further trust in youth and turn to the 19-year-old James and again break the record for Chelsea’s youngest line-up in the Premier League era, having already made history with his starting 11 against Sheffield United a fortnight ago.Alternatively, Lampard could stick with Azpilicueta but with a reduced expectation to get high up the pitch, allowing the skipper to focus on what he has always done best – defending. Check out Goal’s Premier League 2019-20 fantasy football podcast for game tips, debate and rivalries.